The present invention is directed to adhesives useful for bonding seams of components useful in electrostatographic, including digital printing apparatuses. In specific embodiments, the present invention is directed to adhesives, which can be used to bond endless flexible seamed belts wherein an image can be transferred at the seam of the belt with little or no print defects caused by the seam. In embodiments, the present invention relates to an adhesive, which can be used to bond mutually mating elements of a seam, wherein the adhesive comprises a polyamide with an electrically conductive filler dispersed or contained therein. Preferably, the filler is an electrically conductive filler such as a carbon filler, a metal oxide filler, a polymer filler, a charge-transporting molecule, or a mixture thereof. The adhesive provides, in embodiments, a seam with increased strength because the adhesive is crosslinked. However, a belt including the adhesive is still flexible enough to withstand 180xc2x0 crease without cracking. In embodiments, the adhesive provides a seam in which the height differential between the seam and the rest of the belt is virtually nil. The adhesive provides a belt, which in embodiments, allows for image transfer at the seam. This cannot be accomplished with known seamed belts. Image transfer is accomplished partly because the present adhesive possesses the desired conductivity and release properties required for sufficient transfer. The present adhesive also provides, in embodiments, a ripple-free seam. Further, in embodiments, the seam can be rapidly cured at relatively low temperatures. In addition, the adhesive seam, in embodiments, is resistant to alcohol and organic solvents. Moreover, in embodiments, there is no tenting in the seam area due to the adhesive. The adhesive seam, in embodiments, can withstand repeated electrical transfer cycles and remain functional. In embodiments, the adhesive withstands temperature transients between 25 and 130xc2x0 C., and is resistant to ambient changes in relative humidity. The adhesive seam is virtually to totally invisible to the xerographic imaging process.
In a typical electrostatographic reproducing apparatus such as an electrophotographic imaging system using a photosensitive member, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of a developer mixture. One type of developer used in such printing machines is a liquid developer comprising a liquid carrier having toner particles dispersed therein. Generally, the toner is made up of resin and a suitable colorant such as a dye or pigment. Conventional charge director compounds may also be present. The liquid developer material is brought into contact with the electrostatic latent image and the colored toner particles are deposited thereon in image configuration.
In a more typical electrostatic reproducing apparatus, the developer consists of polymeric coated magnetic carrier beads and thermoplastic toner particles of opposite triboelectric polarity with respect to the carrier beads. This is the dry xerographic process.
The developed toner image recorded on the imaging member is transferred to an image receiving substrate such as paper via a transfer member. The toner particles may be transferred by heat and/or pressure to a transfer member, or more commonly, the toner image particles may be electrostatically transferred to the transfer member by means of an electrical potential between the imaging member and the transfer member. After the toner has been transferred to the transfer member, it is then transferred to the image receiving substrate, for example by contacting the substrate with the toner image on the transfer member electrostatically or under heat and/or pressure.
Transfer members enable high throughput at modest process speeds. In four-color photocopier or printer systems, the transfer member also improves registration of the final color toner image. In such systems, the four component colors of cyan, yellow, magenta and black may be synchronously developed onto one or more imaging members and transferred in registration onto a transfer member at a transfer station.
In electrostatographic printing and photocopy machines in which the toner image is transferred from the transfer member to the image receiving substrate, it is desired that the transfer of the toner particles from the transfer member to the image receiving substrate be substantially 100 percent. Less than complete transfer to the image receiving substrate results in image degradation and low resolution. Complete transfer is particularly desirable when the imaging process involves generating full color images since undesirable color deterioration in the final colors can occur when the color images are not completely transferred from the transfer member.
Thus, it is desirable that the transfer member surface has excellent release characteristics with respect to the toner particles. Conventional materials known in the art for use as transfer members often possess the strength, conformability and electrical conductivity necessary for use as transfer members, but can suffer from poor toner release characteristics, especially with respect to higher gloss image receiving substrates.
Polyimide substrate transfer imaging members are suitable for high performance applications because of their outstanding mechanical strength and thermal stability, in addition to their good resistance to a wide range of chemicals. However, the high cost of manufacturing unseamed polyimide belts has led to the introduction of a seamed belt. Even polyimides with the best mechanical and chemical properties often exhibit poor adhesion at the seam even when commercially available primers and adhesives are used.
In the electrostatic transfer applications, use of a seamed transfer polyimide member results in insufficient transfer in that the developed image occurring on the seam is not adequately transferred. This incomplete transfer is partially the result of the difference in seam height to the rest of the belt. A xe2x80x9cbumpxe2x80x9d is formed at the seam, thereby hindering transfer and mechanical performance. The development of puzzle cut seams has increased the quality of transfer somewhat, by decreasing the seam height, thereby allowing smooth cycling. However, even with the improvements made with puzzle cut seams, quality imaging in the seamed area has not been obtainable at present due, in part, to contrast in transfer caused by differences in electrical and release properties of known seaming adhesives. Further, current adhesives do not provide sufficient bonding strength at the seam, resulting in short belt life. In addition, the seam must have the appropriate surface properties in order to allow for sufficient toner release at the seam.
Currently, overlap, puzzle cut, and other seam adhesives consist of uv-curable epoxies and hot-melt adhesives. While these adhesives exhibit acceptable strengths at room temperature under tensile load, most undergo premature failure at elevated temperatures. Additionally, the existing adhesives have been found to perform poorly under some important dynamic test conditions. Because the adhesive seam is not imageable, most machines do not develop images on the seam area, or non-seamed belts are used.
Improved seam adhesives such as polyamic acid adhesives, have proven to be strong. However, adhesives such as polyamic acid adhesives require long cure times at elevated temperatures (for example, 1 hour at 200xc2x0 C.) with loss of water as the polyimide seam is formed. The resulting differential shrinkage causes ripples as the adhesive cures and the cured seams are not completely filled with adhesive. If one side of the puzzle cut seam is glued, tenting occurs. If both sides of the puzzle cut seam are treated with polyamic acid adhesive, ripples form. Such ripples in the seam cause uneven development and ultimately result in print defects, and a reduced belt life. Thus, adhesive alternatives to polyamic acid must be considered.
Therefore, it is desired to provide an adhesive system useful to seam puzzle cut seamed belts, wherein the height differential between the seam and the rest of the belt is virtually nil, and the occurrence of ripples and tenting in the seam is reduced or eliminated. It is further desirable to provide an adhesive that has a low temperature rapid cure in order to increase production of the belts at a reduced production cost. It is also desirable to provide an adhesive that is resistant to alcohol and organic solvents. Further, it is desired to provide an adhesive having electrical, mechanical and toner release characteristics that closely match those of the substrates. Also, it is desirable to provide an adhesive which is able to withstand transients in temperatures between 25 and 130xc2x0 C., and which is resistant to humidity changes. In addition, it is desirable to provide an adhesive seam, which is imageable; thereby reducing or eliminating the presence of print or copy defects. It is desirable to have a low temperature-curing adhesive to eliminate ripple and substrate defects due to differential shrinkage of the belt and adhesive. Moreover, it is desirable to provide an adhesive, which allows for a belt flexible enough to withstand 180xc2x0 bend or crease without cracking, yet strong enough to withstand multiple cycling.
U.S. Pat. No. 5,549,193 relates to an endless flexible seamed belt comprising puzzle cut members, wherein at least one receptacle has a substantial depth in a portion of the belt material at the belt ends.
U.S. Pat. No. 5,721,032 discloses a puzzle cut seamed belt having a strength-enhancing strip.
U.S. Pat. No. 5,487,707 discloses a puzzle cut seamed belt having a bond between adjacent surfaces, wherein an ultraviolet cured adhesive is used to bond the adjacent surfaces.
U.S. Pat. No. 5,514,436 relates to a puzzle cut seamed belt having a mechanically invisible seam, which is substantially equivalent in performance to a seamless belt.
Embodiments of the present invention include: an adhesive comprising a polyamide and an electrically conductive filler.
In addition, embodiments of the present invention include: an adhesive comprising an alcohol soluble polyamide and an electrically conductive filler.
Embodiments further include: an adhesive comprising a polyamide having the following general formula: 
wherein R is selected from the group consisting of hydrogen; alkyl having from about 1 to about 20 carbons, alkoxy having from about 1 to about 20 carbons, alkyl alkoxy having from about 1 to about 20 carbons, and alkylene alkoxy having from about 1 to about 20 carbons, and wherein n is a number of from about 50 to about 1,000.